Control strips
Action to Take When Control
Limits Are Exceeded
When you are interpreting control value plots,
your first consideration should be to determine
whether a plot has exceeded the action limits or
control limits. As long as the plots fluctuate within
action limits, the process is running in control and
generally should be left alone. If a red, green, or blue
measurement exceeds the action or control limits,
verify the readings, check the process, and
immediately process another control strip. When the
results confirm those of the first strip, proceed as
follows.
An out-of-control situation is serious; therefore, it
is important that the information indicating such a
condition is correct. When the out-of-control
condition is verified by a second control strip, it must
be considered real. Two consecutive control strips
seldom provide similar false information about a
process.
Processing trends and tendencies are not as well
defined as control values, but they are equally
important. These conditions in the process indicate
unnecessary bias or drift away from the mean. For
example, when successive plots of control values
show that an increasing number of densities are
moving away from the mean in a particular direction,
you must take corrective action to stop or reverse the
trend before plots have moved beyond the control
limit. Also, processing conditions that cause control
values to plot consistently within but near a control
limit are acceptable.
Each of Kodak’s Z-series manuals has a section
devoted to possible causes of processing problems and
visual references of how they appear on a control
chart. Diagnostic charts are also provided to give
possible causes that can affect the process and what
action to take in each instance. Each specific
monitoring manual includes verbal descriptions of
problems and lists possible solutions.
PHYSICAL QUALITY
The quality assurance and monitoring methods in
this chapter discussed sensitometric aspects because
they are quite complex. Physical quality, however, is
equally important. It is good practice to monitor
physical quality along with image quality by a
methodical examination of control strips and finished
work. The appearance of scratches, digs, spots, or
streaks indicates a mechanical malfunction somewhere
in the processing cycle (fig. 2-19). In many cases, the
causes of these defects are self-evident, and often a
bypass test can isolate the malfunction.
2-37
